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"I recall a staff nurse said that blood sugar was 5 or 6, one of those two numbers ... We therefore concluded that she was not suffering a hypoglycaemic episode or a hypotensive," he said.

Blood tests were also conducted by the team at about the same time.

"It was just a nursing assessment that I was doing. It wasn't something that anybody needs to be alerted [to]," the nurse said when cross-examined by Bills' daughter Michelle Maher over the glucometer test.

"It perplexes me," Maher said, continuing to question the nurse about the glucometer reading of 6.4 mmol/L, well within the normal range of four to 11.

However, when Bills' blood tests came back it showed a clear discrepancy to the nurse's bedside test and indicated the blood sugar levels were critically low and the reason for the sharp drop in health.

The nurse said they only learned of the inconsistency between the tests "way down the track".

But, the court has heard the nurse was informed just hours later.

"You were made aware of that on the same shift, on that same night," Maher said to the nurse.

"I cannot explain what - what I'm trying to say is I cannot recall having this conversation," the nurse replied.

Maher then asked the nurse what her immediate reaction was to low blood sugar being found to be the cause of decline.

"What did you do?" Maher asked,

"You're asking me how did I feel?" the nurse replied.

"No, what was your response?" Maher said.

"I would've been surprised to hear that," the nurse said.

An emotional Maher said the glucometer reading was the "one thing that could prove that [the nurse] acted appropriately" and that notifying doctors "could have saved her [mum's] life".

However, there is no material record of the nurse's glucometer reading.

Despite the glucometers being able to show the results of the more than 400 most recent readings, none displayed the nurse's 6.4 reading at 1.40am, police and DHB investigations found.

The court heard that the blood glucose reading may have been an error.

"Could be several reasons," the nurse said, adding the error may have been because Bills' hand or finger was not cleaned properly.

The nurse said an accurate reading could've saved Bills' life.

"I'm sorry," the nurse said.

Maher asked the nurse if she was aware of the use of insulin around the world to assist is "mercy killings".

"No," replied the nurse.

"Did you inject my mum?" Maher continued.

She was given a warning by chief coroner Judge Deborah Marshall - and the line of questioning was objected to by the nurse's counsel, Karen Rose.

WHERE TO GET HELP:

If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.